Honda 4-Stroke Outboard Engine Parts - Up-300 Series

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This page is for Honda 4-Stroke 300 HP outboard engines. Use it to find compatible parts and service information, including maintenance tips, common replacement parts, and troubleshooting guidance. You can also browse the main Honda collection for a wider selection. Scroll to the bottom of this page to start browsing parts for this engine, and remember that on the collection page you can use the “Filter & Sort” controls to narrow results by horsepower, year range, and part category.

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How to Identify Your 300 HP Model

Locate the nameplate/serial plate on the starboard transom bracket or swivel bracket; it lists the model code and a serial number.
Honda model codes typically start with “BF” followed by horsepower and suffix letters for shaft length (L/XL/XXL), control type, and other options.
Confirm it’s a 4-stroke by noting the engine oil dipstick and oil fill cap under the cowling.
High-power platforms can vary by year (electronics, mounts, gear ratio). Use the exact model and serial number to verify parts.

Engine Overview

High‑Power EFI 4‑Stroke Platform (300 HP class)

Feature	Description
Configuration	Electronic fuel injection 4-stroke, high-output alternator; drive-by-wire controls (iST) available on certain models/years.
Common Models	300 HP class BF-series models (verify exact model code and suffix for parts compatibility).
Advantages	Strong mid‑range torque, smooth shifting with iST, quiet operation, robust charging for electronics.
Notes	Mounting hardware, gear ratios, prop fitment, and control systems may differ by year and shaft length; always match by model code and serial range.

Routine Maintenance & Service Parts

Intervals below are general guidelines for typical pleasure use. Always follow your official Honda service manual for model‑specific procedures and intervals.

Item	Interval*	Remarks	Parts Link
Engine oil + filter	After break‑in, then every 100 hours or annually	Use marine‑rated oil meeting Honda specs; replace crush washer if applicable.	Oil Filters
Gear oil (lower unit)	Every 100 hours or annually	Inspect magnetic drain plug for metal; replace seals if water intrusion is found.	Honda Outboard Parts
Spark plugs	Inspect every 100; replace ~200 hours or as needed	Check gap and coil boots; replace sooner for misfire or fouling.	Spark Plugs
Fuel filter / water separator	Every 100 hours or annually	Drain/replace more often with ethanol fuel or contamination.	Fuel Filters
Water pump impeller / kit	Every 2 seasons or ~200 hours	Replace sooner for weak telltale, overheat alarms, or sandy/silty use.	Honda Water Pump Repair Kits
Anodes (internal/external)	Inspect every 50 hours; replace when 50% depleted	Use the correct material for your water (zinc/brackish, aluminum/salt, magnesium/fresh).	Anodes
Lower unit seal inspection/refresh	As needed (if water found in gear oil)	Replace shift shaft, prop shaft, and driveshaft seals to prevent water intrusion.	Honda Lower Unit Seal Kits

Frequently Used Parts Categories

Routine Service: Service & Maintenance Kits
Cooling System: Honda Water Pump Repair Kits
Fuel System: Fuel Filters and Fuel Pumps
Ignition / Electrical: Electrical Items and Starters
Corrosion Protection: Anodes
Propulsion: Propellers and Propeller Guards
Gearcase Sealing: Honda Lower Unit Seal Kits

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak telltale stream or overheat alarm	Inspect intake screens for debris, verify thermostat operation, check impeller condition.	Water pump kit, intake screen, thermostat, anodes (to reduce corrosion).
Poor acceleration or power loss	Check prop condition/pitch, replace fuel filter, inspect plugs, look for water in fuel.	Propeller, fuel filter, spark plugs.
Hard starting or rough idle	Confirm battery voltage/grounds, replace spark plugs if fouled, inspect fuel quality and filters.	Spark plugs, fuel filter, starter/battery cables.
Gearcase noise or metal in gear oil	Change gear oil, check for water intrusion, inspect seals and prop shaft for fishing line.	Lower unit seal kit, gear oil drain/vent seals, propeller hardware.

FAQs

Are parts interchangeable between different years or platforms?

Not always. High‑power models can change mounts, gear ratios, cowlings, sensors, and control systems by year. Match parts to your exact model code, suffix, and serial range for best results.

When should I replace the water pump impeller?

As a rule of thumb, replace every 2 seasons or ~200 hours, and sooner if you see a weak telltale stream, overheat alarms, or if you run in sandy/silty water.

How often should I change lower unit gear oil?

Typically every 100 hours or annually. Inspect the oil for milkiness (water) or metal shavings; address seal issues immediately if contamination is found.

What information helps confirm part compatibility?

Provide the model code, serial number, shaft length (L/XL/XXL), control type (mechanical or iST), and any notable features. Photos of the nameplate and the part you’re replacing are also helpful.

Ready to find parts by horsepower, year, and model? Browse our main Honda collection to get the right fit for your 300 HP outboard.

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If you’re unsure about your model, send us a photo of the nameplate and the part you need and we’ll help verify compatibility.